Brain wave measuring apparatus

ABSTRACT

In brain wave measuring apparatus comprising at least two electrodes adapted to be contacted against the skin of a living body and an amplifier with its inputs connected to the electrodes, serially connected impedances of equal values are connected across the inputs of the amplifier and a source of check signal is provided to be connectable to the juncture between the impedances.

United States Patent [191 Tateno 1 May 15, 1973 [54] BRAIN WAVEMEASURING [56] References Cited APPARATUS UNITED STATES PATENTS [75]Inventor: Keiji Tateno, Nakano-ku, Tokyo,

Japan 3,602,215 8/1971 Pavnell ..128/2.06 B 2,748,202 5/1956 McCallisteret al...... [73] Assignee: Nihon Kohden Kogyo, Ltd., Tokyo, 3,604,4119/1971 Schuler ..128/2.1 B

Japan Primary ExaminerWilliam E. Kamm [22] 1971 A tt0rney-Chittick,Pfund, Birch, Samuel & Gauthier [21] App]. No.: 111,540

[57] ABSTRACT 30 Foreign Application p i Data In brain wave measuringapparatus comprising at least two electrodes adapted to be contactedagainst the Feb. 2, 1970 Japan ..45/8577 skin of a living body and anamplifier with its inputs connected to the electrodes, seriallyconnected im- [52] US. Cl. ..l28/2.l B pedances of equal values areconnected across the i [51] Int. Cl. ..A6lb 5/00 puts of the amplifierand a Source of check Signal is [58] Field of Search ..l28/2.06 B, 2.06E, provided to be connectable to the juncture between l28/2.06 R, 2.1 B,2.1 E, 2.1 R the impedances 7 Claims, 3 Drawing Figures 1; R1 14 WVW /lBRg N is RECORDER 17 Kg W f (112 15 21 Re 2 16 use PATENTED MY 1 75 SHEET1 OF 2 FIG] PR/OR ART REGDRIJER METER F/az BEEUHDER INVENTOR KEIJITA'IEMJ BY WiPWE &,

& ATTORNEYS BACKGROUND OF THE INVENTION This invention relates to brainwave measuring apparatus, and more particularly to novel brain wavemeasuring apparatus capable of checking the magnitude of the contactresistance difference of electrodes contacted with a living body,particularly a human body, without interrupting the brain wavemeasurement.

Generally, a conventional brain wave measuring apparatus comprises aplurality of electrodes adapted to be contacted against a living body,an amplifier for amplifying brain wave signals picked up by theelectrodes and a brain wave recorder for recording the output from theamplifier. Among the signals applied to the amplifier are included thebrain wave signals to be measured, signals not desired for the brainwave measuring apparatus such as AC hum signals, cardio-signals createdby cardio-clectromotive forces or othernoise signals. For this reason,in order to satisfactorily discriminate the brain wave signals fromanother undesirable signals it is important to increase thediscrimination ratio of the amplifier and the input circuits.

Before describing the subject matter of the invention, thediscrimination ratio will first be discussed with reference to FIG. 1which shows a connection diagram of a prior art brain wave measuringapparatus In this figure, reference characters 1 and 2 show contactresistances of electrodes assumed to have resistance values of R and Rrespectively. These resistances are connected to input terminals of anamplifier 3 whose out-v put is supplied to a brain wave recorder 4.Numerals 5 and 6 show a source of brain wave signal e, generated by ahuman body and a source of noise e other than the brain wave. Inputresistors 7 and 8, each having a resistance of R,, are connected inseries across input terminals of amplifier 3, the juncture between theseresistors being grounded. Supposing an ideal amplifier, theamplification degrees wherein signals e, and e, are in phase andopposite phase on the input circuit of the amplifier are given byfollowing equations.

The output voltage E of opposite phase signals }A-c,, if

then

Since the discrimination ratio is generally given by v M, if 3 we haveon/ m 2 l)/ a Accordingly, where a condition R R is satisfied it ispossible to stabilize the recording operation of the brain waves.Actually however, it is impossible to make equal the contact resistancesat various electrodes.

thus, even when R is not equal to R if the values of these resistanceswere reduced sufiiciently, the ratio E /E could be made small thusenabling stable recording of the brain waves. For this' reason, effortshave been made to improve the method of mounting the electrodes on theliving body or to decrease the contact resistance by applying a pasteonto the skin of the living body. However, a plurality of electrodes,for instance 24 electrodes, are required to be used for the measurementof the brain waves and it is'difficult to decrease the contactresistancesof all electrodes.

Moreover, as the measurement of the brain waves is made while the livingbody is maintained quiet for a long time, the contact condition betweenthe electrodes and the skin is impaired by the drying of the paste or bythe movement of the living body, thus increasing the contact resistance.Such increase in the contact resistance results in the abnormal waveformof the recorded brain waves, and it is difficult to determine whethersuch abnormal waveform is caused by the increase in the electroderesistance or by the abnormal condition of the brain wave per se. Inorder to make a correct judgement it has been the practice to interruptthe recording operation of the brain waves to check the magnitude of thecontact resistances of the respective electrodes. More particularly,after stopping the operation of the recorder 4 of the brain wavemeasuring apparatus shown in FIG. 1, source 9 is connected to aresistance meter 10 by closing a switch 11. Then current is passed toelectrode 1 or 2 through a transfer switch 12 to determine whether theabnormal waveform represented by the deflection of resistance meter 10is caused by the increase in the contact resistance or not and a checkis made as to which one of the electrodes has increased its contactresistance. Thus, such a prior method of measurement requires theinterruption of the recording of the brain waves and the operation ofthe transfer switch 12, and is not efficient. Although in FIG. 1, abattery 9 is used as the source for checking, a source ofalternatingcurrent can also be used.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide an improved brain wave measuring apparatus by which uponoccurence of an abnormal waveform in the recorded brain waves thedifference between contact resistances of a plurality of electrodes canbe checked promptly without the necessity of interrupting the recordingoperation of the brain waves.

Another object of this invention is to provide an improved brain wavemeasuring apparatus capable of checking the difference between contactresistances of a plurality of electrodes by utilizing a single switch.

Further object of this invention is to provide a novel brain wavemeasuring apparatus capable of measuring the brain waves superposed upona checking signal from an AC oscillator even while the contactresistances of the electrodes are being checked.

A still further object of this invention is to provide a brain wavemeasuring apparatus capable of readily recording stable brain waves bydetecting a signal proportional to the discrimination ratio between anamplifier and its input circuit for determining the difference in thecontact resistances of a plurality of electrodes and by compensating forthe diflerence in the contact resistances.

According to one aspect of this invention, there is provided brain wavemeasuring apparatus comprising a first electrode with one end contactwith the skin of a living body, a second electrode with one endcontacted with the skin of the living body, amplifier means having twoinput terminals respectively connected to the other ends of the firstand second electrodes, brain wave recording means connected to theoutput terminal of the amplifier means, a series circuit including twocheck signal supply impedances of equal value, the series circuit beingconnected across the two input terminals of the amplifier means, and asource of check signals connectable to the common juncture between thecheck signal supply impedances.

According to another aspect of this invention there is provided brainwave measuring apparatus comprising a plurality of electrodes with theirends contacted with the skin of a living body, a plurality ofamplifiers, each having two input terminals connected with the otherends of the electrodes, a plurality of brain wave recording meansrespectively connected to the outputs of the amplifiers, a source ofcheck signals, and a plurality of check signal supply impedances ofequal impedance value connected between the source of check signals andrespective ones of the other ends of the electrodes.

BRIEF DESCRIPTION OF THE DRAWING Further objects and advantages of theinvention will be more clearly understood from the following descriptionwhen taken in conjunction with the accompanying drawings in which:

FIG. 1 is a connection diagram of a prior art brain wave measureingapparatus;

FIG. 2 shows a connection diagram, partly in block form, of oneembodiment of the novel brain wave measuring apparatus and FIG. 3 is aconnection diagram, partly in block form, of a modified embodiment ofthis invention.

FIGS. 2a and 3a are partial views of modifications of FIGS. 2 and3,respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows one embodiment ofthe novel brain wave measuring apparatus in which elements correspondingto those shown in FIG. 1 are designated by the same reference numerals.For the sake of description, the source of noise signal 6 (e shown inFIG. 1 has been omitted from FIG. 2. In the embodiment shown in FIG. 2,a high input impedance amplifier 13, is provided having input terminals14 and 15. Ends of electrodes 1 and 2 are connected to the skin of aliving body (not shown) or a source of the brain wave signal whereas theopposite terminals of the electrodes are connected to input terminals 14and 15 of amplifier 13. A series circuit comprised by resistors 16 and17 of the equal resistance value R is connected across input terminalsl4 and 15 and the juncture 18 between these resistors is connected to anAC oscillator 20 for checking via a switch 19. The neutral point of thesource of the brain wave signal 5 is grounded through a groundingelectrode 21 having resistance R When switch 19 is closed to connectchecking oscillator 20 to the juncture 118, the output voltage E, fromamplifier 13 can be expressed by the equation where g represents theoutput voltage of checking oscillator 20.

The output voltage E expressed by equation 4 is proportional to thediscrimination ratio shown by equation 3 so that so long as theamplification degree A and output voltage g are constant, output voltageE, becomes a function of the discrimination ratio.

In other words, while switch 19 is being closed when an abnormalwaveform is recorded by recorder 4 during the measurement of the brainwave, the output voltage E will manifest a large amplitude if theabnormal waveform is caused by the increase in the contact resistancedifference of the electrodes. On the other hand, if such abnormalwaveform is not caused by the increase in the contact resistancedifference of the electrodes but instead caused by the defect of thebrain, the waveform of the output voltage E, would not vary by theclosure of switch 19 unless otherwise the contact resistance of theelectrode varies from the initial value at the time of mounting theelectrodes. In this manner, this invention permits one to determinewhether the abnormal waveform is caused by the variation in the contactresistance of the electrode or not while the recording operation of thebrain waves is being continued. If it were determined that the abnormalwaveform is caused by the electrodes, the contact condition of the pairof electrodes 1 and 2 against the skin of the living body is adjustedwhile observing the waveform recorded on recorder 4 for obtaining stablerecord of the brain waves.

Generally, it is rare to perform the measurement of one channel by usinga single channel involving two electrodes. There generally are 8 to 16channels and a selected electrode is connected to the amplifier togetherwith a common reference electrode.

FIG. 3 shows a modified brain wave measuring apparatus utilizing twochannels. In this figure, electrodes 1 and 2, amplifier 13 and recorder4 comprise one channel for measuring source of brain wave signal 5 (ewhereas electrodes 2 and 100, amplifier 131 and recorder 41 compriseanother channel for measuring source of the brain wave signal 51 (e,),electrode 2 being utilized in common for two channels. One end of a highresistance 16 is connected to input terminal 14 of amplifier 13 and thecorresponding end of another high resistance 17 is connected to thejuncture between input terminals 15 and 141 of amplifiers 13 and 131,respectively. Further, one end of high resistance 18 is connected toinput terminal 151 of amplifier 131 and the opposite ends of these highresistors are commonly connected to switch 19. These resistors l6, l7and 18 which act to supply check signals having equal resistance value R5 megohms for example. An electrode In the same manner output voltage Eof amplifier 131:

where A and A represents the amplification degrees of amplifier l3 and131, respectively.

Equations (5) and (6) show that even with a brain wave measuringapparatus of the multi-channel construction relations similar to that ofFIG. 2 also hold true so that check signals are converted into signalsproportional to discrimination ratios and appear simultaneously as theoutputs of respective channels. For this reason, this inventioneliminates the trouble of checking respective electrodes by manipulatingthe transfer switch.

According to this invention it is possible not only to check the contactcondition of the electrode without the necessity of interrupting therecording operation of the brain waves but also to simultaneously checkthe contact condition of a plurality of electrodes by using a singleswitch. Further, by connecting ends of a plurality of resistors forsupplying check signals to respective electrodes and by connecting theother ends of these resistors to a common source of check signals, evenwhen a plurality of amplifiers are commonly connected to one electrodeas shown in FIG. 3, it is possible to measure the brain waves at highaccuracies because these input resistors are not connected in parallelwith respect to the amplifiers. Although in the above describedembodiments resistors are utilized as the circuit elements for supplyingthe check signals, if desired, the check signals may be supplied torespective electrodes through coupling transformers.

What is claimed is:

1. An apparatus for measuring the brain waves of a living bodycomprising a first electrode with one end adapted to be contacted withthe skin of said living body, a second electrode with one end adapted tobe contacted with the skin of said living body, amplifier means havingtwo input terminals respectively connected to the other ends of saidfirst and second elec trodes, recording means for recording brain waveand signals resulting from a difference in contact resistance of saidfirst and second electrodes and connected to the output terminal of saidamplifier means, a series circuit including two check signal supplyimpedances of equal value, said series circuit being connected acrosssaid two input terminals of said amplifier means, and a source of checksignals connectable to the common juncture between said check signalsupply impedances.

2. The brain wave measuring apparatus according to claim 1 which furthercomprises a switch connected between said common juncture of said checksignal supply impedances and said source of check signals.

3. The brain wave measuring apparatus according to claim 1 wherein saidsource of check signals comprises an AC signals oscillator.

4. The brain wave measuring apparatus according to claim 1 wherein saidcheck signal supply impedances comprise resistors.

5. An apparatus for measuring the brain waves of a 7 living bodycomprising a plurality of electrodes with their ends adapted to becontacted with the skin of said living body, a plurality of amplifiers,each having two input terminals connected with the other ends of saidelectrodes, a plurality of recording means for recording brain wave andsignals resulting from a difference in contact resistance of saidelectrodes and respectively connected to the outputs of said amplifiers,a source of check signals, and a plurality of check signal supplyimpedances of equal impedance value connected between said source ofcheck signals and respective ones of said other ends of said electrodes.

6. The brain wave measuring apparatus according to claim 5 wherein saidimpedances comprises resitors.

7. The brain wave measuring apparatus according to claim 5 wherein saidsource of check signals comprises an AC signals oscillator.

"dam-x2049) o o- 1 vvr uscoMM-pc avg-pas 3,732,859 Dated May 15, 1973Patent No- Inventor(s) Kei-ij 'Fa'l-m'm It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 4-; "R R R R R- R v e (R R lines 9 and 10 g g 9 eg; l

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lines 12' and. 13, g l 2 s I 9 1 2 e and R R R should D63 M, 1f R R R RR 2 I Rl' Signed and sealed jshis 22nd day of January 19714..

(SEAL) I Attest: I

EDWARD M0 FLETCHER, JR. RENE D. 'IEGI'MEYER Attesting Officer ActingCommissioner of Patents

1. An apparatus for measuring the brain waves of a living bodycomprising a first electrode with one end adapted to be contacted withthe skin of said living body, a second electrode with one end adapted tobe contacted with the skin of said living body, amplifier means havingtwo input terminals respectively connected to the other ends of saidfirst and second electrodes, recording means for recording brain waveand signals resulting from a difference in contact resistance of saidfirst and second electrodes and connected to the output terminal of saidamplifier means, a series circuit including two check signal supplyimpedances of equal value, said series circuit being connected acrosssaid two input terminals of said amplifier means, and a source of checksignals connectable to the common juncture between said check signalsupply impedances.
 2. The brain wave measuring apparatus according toclaim 1 which further comprises a switch connected between said commonjuncture of said check signal supply impedances and said source of checksignals.
 3. The brain wave measuring apparatus according to claim 1wherein said source of check signals comprises an AC signals oscillator.4. The brain wave measuring apparatus according to claim 1 wherein saidcheck signal supply impedances comprise resistors.
 5. An apparatus formeasuring the brain waves of a living body comprising a plurality ofelectrodes with their ends adapted to be contacted with the skin of saidliving body, a plurality of amplifiers, each having two input terminalsconnected with the other ends of said electrodes, a plurality ofrecording means for recording brain wave and signals resulting from adifference in contact resistance of said electrodes and respectivelyconnected to the outputs of said amplifiers, a source of check signals,and a plurality of check signal supply impedances of equal impedancevalue connected between said source of check signals and respective onesof said other ends of said electrodes.
 6. The brain wave measuringapparatus according to claim 5 wherein said impedances comprisesresitors.
 7. The brain wave measuring apparatus according to claim 5wherein said source of check signals comprises an AC signals oscillator.